They lack a nucleus. Scattered cells can also be seen in the blood. The grayish color of the cytoplasm is due to its increase number of RNA moelcules since these cells are still less mature than the fully mature RBC
Note: As Erythroid precursors mature, the color of their cytoplasm changes from blue to gray to red-orange (this is due to the increase in the number of hemoglobin molecules within the red cells).